WASHINGTON — Twelve Republican and Democratic senators are calling on the Pentagon to cancel all contracts to buy helicopters for Afghan security forces from a state-run Russian arms exporter that is a top weapons supplier to the Syrian government.

The lawmakers led by Republican Sen. John Cornyn (KOHR'-nihn) of Texas sent a letter on Monday to Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff. The senators joined more than 80 House members who oppose the $572 million deal for 30 Russian-made Mi-17 helicopters from the company (Rosoboronexport).

The lawmakers said the arms exporter has transferred weapons and ammunition to the government of Syrian President Bashar Assad (bah-SHAR' AH'-sahd). The senators said the helicopter deal puts U.S. taxpayers in the "repugnant position" of subsidizing the murder of Syrian civilians.